1. Field
The disclosed embodiments relate to means for connecting pieces of avionics equipment on board an aircraft by means of an optical communication bus network when these pieces of equipment have been designed for communication via an electrical bus network, without it being necessary to modify said pieces of avionics equipment.
2. Brief Description
Current civil airplanes depend greatly on digital technologies. Various pieces of equipment having an electronic communication interface, such as computers or other pieces of equipment provided with microprocessors, microcontrollers or digital interfaces, fulfill drive, control and monitoring functions on board the aircraft and exchange information over digital buses.
Buses employed most are electrical buses using cables with a core made of a conducting metal, generally copper or aluminum. The digital data is then transmitted in the form of variations in electrical voltage. The technology of electrical buses, in particular serial buses in which coded information is transmitted in succession on the same physical medium, is justified, in particular by the reliability of the connection means on board aircraft that are subjected to severe operational environments. However, these electrical buses have the drawback of being relatively heavy and sensitive to electromagnetic interference.
The requirement, especially for operational interchangeability reasons, for high stability in the definition of the equipment employed on board airplanes, in particular at their physical and functional interfaces, has lead aircraft manufacturers to normalize the mechanical and electrical interfaces of this equipment.
The aeronautics world is for example very familiar with the ARINC 429 standard, which defines in detail the interfaces and protocols for communication between pieces of equipment on board airplanes by means of one-way buses that meet this standard.
More recently, simplification of the physical buses has been made possible by increasing the data rates that these buses are capable at the present time of supporting with the reliability conditions necessary for aeronautical applications. Thus, several one-way buses operating at relatively modest data rates used in systems in accordance with the ARINC 429 standard may be replaced by a two-way bus with a high data rate, for example one hundred megabytes per second. These high data rate two-way buses are associated with new standards and, of course, with new communication interfaces for avionics equipment.
These new interfaces are at the present time still associated with electrical communication buses for the operational reliability reasons mentioned above.
FIG. 1 shows an architecture for a number of pieces of on-board electronic equipment connected via a high data rate electrical bus.
In this example, computers 1a, 1b, 1c are connected, via electrical communication buses 4a, 4b, 4c respectively, to a switch 2 which is a piece of equipment capable of switching electrical signals from one bus to another according to address signals arriving on the bus itself. Other pieces of equipment 3a, 3b, for example sensors or actuators, are connected directly to the computers 1a, 1b, respectively, by means of electrical communication buses 5a, 5b respectively.
Simultaneous two-way electrical communication buses, called full-duplex buses, generally consist of two pairs of electrical conductors, or four-channel cable, each pair being dedicated to one communication direction. In general, each pair is twisted, and the cable thus formed has a shield intended to protect the cable from electromagnetic interference coming from the outside and also to protect the external environment from the electromagnetic radiation that might be transmitted by the cable. These cables frequently have a mass per unit length of around 40 to 50 g/m. The cable is equipped at each of its ends with connectors comprising four electrical contacts, these being male or female contacts depending on the requirement, with the shielding taken up onto the metal structure of the connector. The ARINC 600 standard (see supplement 14, appendix 20 of the provisional addition of 15 Jul. 2003) describes electrical and mechanical characteristics of such a four-channel connector. In these connectors having four electrical contacts, the two contacts dedicated to transmission are generally called Tx+ and Tx− contacts, and the two contacts dedicated to reception are generally called Rx+ and Rx− contacts. The + and − signs remind users that the bus is polarized and that this polarity must be respected when mounting connectors on the electrical cable of the bus.
It is also possible to convert the information to be transmitted into optical signals that can propagate along optical fibers. Optical communication buses, which have advantages in terms of weight per unit length, data rate and electromagnetic radiation insensitivity, are still not widely used in the field of civil transport aircraft because of problems when connecting optical links and because of the current equipment technology which at the present time is predominantly designed to operate with electrical communication buses.